Prior work has documented how dynamic bonds impact stress relaxation and viscosity in polymers, but their role on crystallization is not well understood. Precise ethylene vitrimers with 8, 10, or 12 methylene units between boronic ester junctions were studied to understand the impact of bond exchange on crystallization kinetics and morphology. Compared to linear polyethylene which crystallizes rapidly, a long induction period for crystallization is seen in the vitrimers (100 – 1000 min) and increases with increasing crosslink density, ultimately taking weeks in the densest networks. An increase in melting temperatures (T<sub>m</sub>) of 25-30 K is observed with isothermal crystallization over 30 days. Wide angle x-ray scattering (WAXS) shows an unexpected crystal–crystal transition, which is also tracked with optical microscopy (OM). Control experiments on a precise permanent network indicate that dynamic bonds are facilitating long-time rearrangements of the crystals, which is critical to understand for applications of semi-crystalline vitrimers.

Crystal-crystal transitions and long term evolution of melting temperatures facilitated by dynamic bond exchange in ethylene dynamic networks

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.